[PATCH] PCI: update device mps when doing pci hotplug

[Yijing Wang <wangyijing@huawei.com>]

Currently we dont't update device's mps vaule when doing
pci device hot-add. The hot-added device's mps will be set
to default value (128B). But the upstream port device's mps
may be larger than 128B which was set by firmware during
system bootup. In this case the new added device may not
work normally.

The reference discussion at
http://marc.info/?l=linux-pci&m=135420434508910&w=2
and
http://marc.info/?l=linux-pci&m=134815603407842&w=2

Reported-by: Joe Jin <joe.jin@oracle.com>
Reported-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Cc: Jon Mason <jdmason@kudzu.us>
---
 drivers/pci/probe.c |   49 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index bbe4be7..57d9a5b 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1556,6 +1556,52 @@ static int pcie_bus_configure_set(struct pci_dev *dev, void *data)
 	return 0;
 }
 
+static int pcie_bus_update_set(struct pci_dev *dev, void *data)
+{
+	int mps, p_mps;
+
+	if (!pci_is_pcie(dev) || !dev->bus->self)
+		return 0;
+
+	mps = pcie_get_mps(dev);
+	p_mps = pcie_get_mps(dev->bus->self);
+
+	if (pci_pcie_type(dev->bus->self) != PCI_EXP_TYPE_ROOT_PORT) {
+		/* update mps when current device mps is not equal to upstream mps */
+		if (mps != p_mps)
+			goto update;
+	} else {
+		/* update mps when current device mps is smaller than upstream mps */
+		if (mps < p_mps)
+			goto update;
+	}
+
+	return 0;
+
+update:
+	/* If current mpss is lager than upstream, use upstream mps to update
+	 * current mps, otherwise print warning info.
+	 */
+	if ((128 << dev->pcie_mpss) >= p_mps)
+		pcie_write_mps(dev, p_mps);
+	else
+		dev_warn(&dev->dev, "MPS %d MPSS %d both smaller than upstream MPS %d\n"
+				"If necessary, use \"pci=pcie_bus_peer2peer\" boot parameter to avoid this problem\n",
+				mps, 128 << dev->pcie_mpss, p_mps);
+	return 0;
+}
+
+static void pcie_bus_update_setting(struct pci_bus *bus)
+{
+
+	/*
+	 * After hot added a pci device, the device's mps will set to default
+	 * vaule(128 bytes). But the upstream port mps may be larger than 128B.
+	 * In this case, we should update this device's mps for better performance.
+	 */
+	pci_walk_bus(bus, pcie_bus_update_set, NULL);
+}
+
 /* pcie_bus_configure_settings requires that pci_walk_bus work in a top-down,
  * parents then children fashion.  If this changes, then this code will not
  * work as designed.
@@ -1566,6 +1612,9 @@ void pcie_bus_configure_settings(struct pci_bus *bus, u8 mpss)
 
 	if (!pci_is_pcie(bus->self))
 		return;
+
+	/* update mps setting for newly hot added device */
+	pcie_bus_update_setting(bus);
 
 	if (pcie_bus_config == PCIE_BUS_TUNE_OFF)
 		return;
-- 
1.7.1